refactor(arena-two-pick): route entry/finish through InventoryService

Replace RewardGrantService + ICurrencySpendService + IViewerEntitlements with
IInventoryService. tx.IsFreeplay replaces FakeEntitlements.IsFreeplay; debit
helpers take IInventoryTransaction. ComputePostStateRewardList deleted (replaced
by result.RewardList from CommitAsync). Update 5 test files to new 8-arg ctor.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.UnitTests/Services/ArenaTwoPickServiceTopTests.cs

@@ -81,7 +81,7 @@ public class ArenaTwoPickServiceTopTests
     private static IArenaTwoPickService BuildService(SVSimDbContext db, IArenaTwoPickRunRepository runRepo)
     {
         // GetTopAsync only uses _runs — every other dep can be null! because the test path
-        // never touches them. The 9th positional arg (db) is required from Task 13 onward.
-        return new ArenaTwoPickService(runRepo, null!, null!, null!, null!, null!, null!, null!, db, null!);
+        // never touches them.
+        return new ArenaTwoPickService(runRepo, null!, null!, null!, null!, null!, null!, db);
     }
 }